A conventional system for dispensing heated adhesive (i.e., a hot-melt adhesive dispensing system) generally includes a melter having a tank or reservoir for receiving adhesive materials in solid or liquid form, a heater grid for heating and/or melting the adhesive materials in the tank or reservoir, and a pump in communication with the heater grid and the tank or reservoir for driving and controlling the dispensation of the heated adhesive from the melter to downstream dispensing guns or modules. One or more hoses may also be connected to the melter to direct the dispensation of heated adhesive to the adhesive dispensing guns or modules located downstream from the pump. Furthermore, conventional dispensing systems generally include a controller (e.g., a processor and a memory) and input controls electrically connected to the controller to provide a user interface with the dispensing system and to control the various components of the dispensing system.
Conventional hot-melt adhesive dispensing systems typically operate at ranges of temperatures sufficient to melt the received adhesive and heat the adhesive to an elevated application temperature prior to dispensing the heated adhesive. As adhesive throughput requirements increase (e.g., up to 20 lb/hour or more), adhesive dispensing systems have traditionally increased the size of the tank or reservoir used with the melter to ensure that the maximum desired flow of molten adhesive can be supplied. However, large tanks and reservoirs result in a large amount of hot-melt adhesive being held at the elevated application temperature within the adhesive dispensing system. During periods of operation when the adhesive dispensing system is not operating at a maximum throughput, large amounts of hot-melt adhesive may be held at the elevated application temperature within the tank or reservoir for significant lengths of time, which can lead to degradation and/or charring of the adhesive, negative effects on the bonding characteristics of the adhesive, clogging of the adhesive dispensing system, and/or additional downtime. Furthermore, the provision of heated hoses extending from the melter to the dispensing modules further increases the complexity and expense of the adhesive dispensing system, while also further increasing the time that the adhesive is held at the elevated application temperature.
In several other conventional adhesive dispensing systems, the tank or reservoir of the melter has been reduced in size or nearly eliminated by providing a different type of melter configured to melt adhesive on demand when required by the dispensing modules (referred to as “melt on demand”). By using melt on demand, some of the problems associated with holding the adhesive at the elevated application temperature for long periods of time are reduced in significance, including but not limited to, charring and degradation. One example of such a melt on demand process is described in U.S. Pat. No. 6,230,936 to Lasko. Although systems such as the one shown in the Lasko patent melt adhesive on an as-needed basis, these systems continue to suffer from re-solidification of adhesive when used during periods of low throughput. It is highly impractical or impossible to expel clogs of re-solidified adhesive from the system when these clogs occur. In addition, the conversion efficiency of the energy applied to the adhesive is lowered by the problems experienced with these systems.
For reasons such as these, an improved hot-melt adhesive dispensing system that maximizes energy conversion efficiency while using melt on demand would be desirable.